Suppression of delayed hypersensitivity to a purified protein (as indicated by intradermal reactions) can be adoptively transferred with splenic cells from a suppressed donor to a hypersensitive recipient. This suppression has also been demonstrated quantitatively in vitro by blastogenesis when splenic cells from sensitized animals are added to sensitized lymph nodes in the presence of antigen. A soluble suppressive factor from spleens of hypersensitive donors and produced with specific antigen can also be demonstrated; such a factor is not present in lymph node cells. BIBLIOGRAPHIC REFERENCES: S.B. Salvin and Ruth Neta. A possible relationship between delayed hypersensitivity and cell-mediated immunity. Amer. Rev. Resp. Dis., 111: 373-377, 1975. Ruth Neta and S.B. Salvin. A suppressor cell in the regulation of delayed hypersensitivity. Proc. Tenth Joint Conference on Tuberculosis, 199-205, 1975.